The invention relates to correcting uniformity characteristics of a cured pneumatic tire.
Pneumatic TIRES
FIGS. 1A and 1B illustrate an exemplary pneumatic tire 100 of the prior art. The tire 100 includes a pair of annular, substantially inextensible beads 102 and 104, each of which is disposed within a respective bead portion 106 and 108 of the tire 100, a generally cylindrical tread portion 110, a relatively inextensible belt structure (xe2x80x9cbeltsxe2x80x9d) 112 disposed within the tread portion 110, and sidewall portions 114 and 116 extending between opposite sides 110a and 110b of the tread portion 110 and respective ones of the bead portions 106 and 108. The tire 100 has a section height SH measured from an edge of the bead portion 106 (or a nominal rim diameter) to an outer diameter of the tread portion 110. The tire 100 has an inner surface 118 and an outer surface 119. An inner liner (not shown) is typically disposed on the inner surface 118 of the tire 100.
At least one carcass reinforcing member 120 (also referred to as a xe2x80x9cplyxe2x80x9d) extends between the two beads 102 and 104, within the carcass of the tire 100. The ply 120 has a central (middle) portion 120a which is disposed between the two beads 102 and 104, and has two opposite end portions (xe2x80x9cturn-upxe2x80x9d ends) 120b and 120c, each of which wrap around a respective one of the beads 102 and 104 and extend radially back toward the tread portion 110 of the tire 100. The tire 100 further typically includes bead filler apexes 122 and 124 disposed atop respective ones of the beads 102 and 104 and extending radially outwardly therefrom.
The tire 100 has an axis of rotation (not shown), an outer diameter which is twice (2xc3x97) a radius dimension between the axis of rotation and the tread surface, and an inner diameter which is (2xc3x97) the radius dimension between the axis of rotation and an inner edge of the bead portion. An equatorial plane xe2x80x9cEPxe2x80x9d for the tire 100, is defined as a plane which is perpendicular to the tire""s axis of rotation and passing through the center of the tread portion 110, or midway between the tire""s beads 102 and 104. A radial direction (orientation) is indicated by the arrow 130, and a lateral (or axial) direction (orientation) is indicated by arrows 132.
The at least one ply 120 of the tire is at least one layer of rubber-coated ply cords. Ply cords are typically formed of cotton, rayon, nylon, polyester or other man-made synthetic or textile cord which are capable of exhibiting permanent changes in physical properties upon application of load or heat, or of fiber glass, metal wire or the like, the physical properties of which are relatively non-changeable upon application of load or heat. Commonly-owned U.S. Pat. No. 4,654,253 (Brown, et al.; 1987) and U.S. Pat. No. 4,763,468 (Brown, et al.; 1988) disclose high strength greige woven fabrics particularly suitable for use as a tire reinforcement component, wherein a cord may comprise at least two optimally drawn polymeric yarns.
Generally, there are three basic types of pneumatic tiresxe2x80x94xe2x80x9cbiasxe2x80x9d, xe2x80x9cbias/beltedxe2x80x9d and xe2x80x9cradialxe2x80x9dxe2x80x94each type essentially being defined by the orientation of the cords within the at least one ply (120).
In the bias (or xe2x80x9ccross-plyxe2x80x9d) tire, the cords of the reinforcing ply extend diagonally across the tire from bead-to-bead, typically at an angle of between 25 and 40 degrees with respect to a centerline of the tire. The cords run in opposite directions in each successive reinforcing ply layer, resulting in a crisscross pattern of cords.
In the bias/belted tire, as in the bias tire, the cords extend diagonally across the tire, from bead-to-bead, typically at an angle of between 25 and 45 degrees with respect to the centerline of the tire, and the cords run in opposite directions in each successive ply. A cord-reinforced xe2x80x9cbeltxe2x80x9d structure is disposed in the tread portion of the tire, and the belt cords typically have an angle of between 20 and 35 degrees with respect to the equatorial plane of the tire.
In the radial tire, the plies of reinforcing cords are parallel and extend transversely from bead-to-bead. That is, the parallel cords are substantially perpendicular to the direction of tire travel.
A cord-reinforced belt structure is disposed in the tread portion of the tire, and is composed of several layers of cords disposed nearly parallel (10 to 30 degrees) to the circumference of the tire. The belt structure acts to restrict the reinforcing plies. Increased sidewall bulging is characteristic of radial tires.
As is disclosed in commonly-owned European Patent Application Publication No. 0 522 468 A1 (published 13.02.93), in a typical tire manufacturing process, an inner liner is disposed on a generally cylindrical tire building drum (or mandrel). At least one carcass reinforcing member (xe2x80x9cplyxe2x80x9d, compare 120) is disposed over the inner liner. Next, bead rings (compare 102, 104) are disposed over the reinforcing ply, and apex rubber (compare 122, 124) is applied over the beads. Next, a turn-up bladder or the like, such as is disclosed in U.S. Pat. No. 5,407,521 (Falvard; 1995), is activated to turn-up the two opposite end portions (compare 120b, 120c) of the ply (and, optionally, the inner liner) around the bead rings. Next, sidewall rubber is added, and the resulting tire xe2x80x9ccarcassxe2x80x9d is shaped into what is generally its ultimate toroidal form. Tread rubber and, optionally, belts or breakers and chafers, may then be added to the construction, and the resulting xe2x80x9cgreenxe2x80x9d tire can be inserted into a mold wherein it is heated for a period of time (e.g., approximately 10-30 minutes) at an elevated temperature (e.g., at least approximately 120 degrees Celsius, such as approximately 150 degrees Celsius) to xe2x80x9ccurexe2x80x9d or xe2x80x9cvulcanizexe2x80x9d the rubber components of the green tire. During the molding process, tread patterns are typically impressed into the tread rubber, and designs, lettering and the like may be formed in the sidewall rubber of the tire. In some cases, tires are retained in the mold until they have become substantially cooled down. More often, tires are removed from the mold without a cooling period, and are allowed to cool down (e.g., to ambient temperature) outside of the mold. Rubber is a poor conductor of heat and the thick tread portion of the tires continue to vulcanize for a period after removal from the molds.
After a tire is assembled and at least partially cured, the tire is typically tested for one or more uniformity characteristics. xe2x80x9cUniformityxe2x80x9d is defined herein as what a xe2x80x9cperfectxe2x80x9d or xe2x80x9cidealxe2x80x9d tire would yield for a certain measured characteristic when tested during rotation. xe2x80x9cUniformity characteristicxe2x80x9d is defined herein as a deviation in those certain characteristics from what the perfect tire would yield during testing.
As is evident, the pneumatic tire is a somewhat complicated construction of various materials which is difficult to manufacture with perfect consistency, from tire-to-tire inconsistencies in materials, in the placement of the materials on the building drum, and other process variables will contribute to both dimensional and dynamic variations, from tire-to-tire.
Generally, a dimensional non-uniformity is a deviation from perfect roundness of the outer circumference of the tire (alternatively, the outer circumference of the tire being round, but off-center with respect to the tire""s axis of rotation), and a dynamic non-uniformity is a condition which manifests itself in the tire""s ability to react forces at different orientations of the tire.
Sources of such tire non-uniformities may include one or more of the following:
a. The tread, sidewall and innerliner are stored on long rolls in the xe2x80x9cgreenxe2x80x9d state and are assembled into a tire in the green state. While in the green state, during storage and tire building, rubber can deform. Therefore, the green rubber tire components may not remain uniformly thick before curing.
b. The beads may deform non-uniformly, since they incorporate a green rubber matrix and are held in position by a deformable green rubber matrix.
c. Before curing, the position of the ply within the tire is fixedly held by the surrounding green rubber. If the green rubber deforms, the ply""s position may be displaced.
d. Where the ply is spliced (overlapped on the build drum), it is doubled over itself, and stiffer than the remainder of the ply.
e. The ply cords may not be laid onto the building drum with uniform straightness and tension, and the two beads may not be positioned perfectly parallel (relative to each other) over the ply on the building drum.
f. In the mold, cord shrinkage and carcass inflation may cause the cords to slip around the beads, but spliced portion(s) of the ply may tend to slip less than unspliced portion(s).
g. If the belt and tread are not positioned symmetrically over the green carcass, the green tire, and hence the cured tire, will not be uniform. The nominally cylindrical belt package may also be somewhat conical.
h. If the green tire is not positioned symmetrically within the mold, the cured tire will not be uniform.
i. In the mold, the inflated bladder tensions (stretches) the ply outward, and the ply""s nylon or polyester fibers shrink when heated, thus tensioning the ply further. Under tension, the ply slips around the bead, possibly to a different extent at different locations around the bead, and a splice slips around the bead least.
j. In the mold, the rubber can xe2x80x9clock upxe2x80x9d (stiffen curing) around the ply at different times at different locations, thus causing nonuniform ply stress.
The degree of dimensional and/or dynamic uniformity in a tire may manifest itself in the tire""s ability to run smoothly and vibration free, as well as in the xe2x80x9chandlingxe2x80x9d of the tire. Therefore, after a tire is manufactured, and before it is sold, it is typically tested for tire uniformity characteristics. A variety of tire uniformity measuring (testing) machines (apparatuses) are known and are described, for example, in U.S. Pat. No. 4,171,641, U.S. Pat. No. 4,458,526, U.S. Pat. No. 5,022,186 and U.S. Pat. No. 5,103,669.
A typical tire uniformity testing process, and representative results obtaining therefrom, are presented in U.S. Pat. No. 5,365,781 (Rhyne; 1994; hereinafter referred to as the ""781 Patent). (See also related U.S. Pat. No. 5,616,859 and U.S. Pat. No. 5,458,176).
As described in the ""781 Patent, an initial force variation of an uncorrected tire, as tested, may be graphically illustrated to represent corresponding electrical signals from a tire uniformity tester. The force variation as a function of circumferential position on the tire, as represented by a waveform, may be decomposed into a series of desired harmonic waveforms. The harmonic waveforms are determined in a computer by a Fourier analysis of the radial force variation waveform sensed during rotation of the tire on the tire uniformity tester. The analysis and waveforms are stored in the computer and referenced to a particular tire. U.S. Pat. No. 3,739,533 also describes known techniques for measuring lateral and/or radial force variations in a pneumatic tire.
FIG. 2A is a graph illustrating a xe2x80x9ccompositexe2x80x9d waveform (force variation curve) 202 such as may be generated by a tire uniformity tester (not shown), for a particular tire (not shown) being tested. The horizontal axis represents the circumferential position (from 0 to 360 degrees) on the tire being tested. The vertical axis represents the amplitude of a measured radial force variation, in any suitable units such as decaNewtons (daN). The composite waveform 202 is representative of the xe2x80x9crawxe2x80x9d data from the tire uniformity tester and, as is evident, there is a variation in radial force as a relatively complex function of circumferential position on the tire. The composite waveform 202 can, in a computer (not shown) be decomposed into a series of any desired number of xe2x80x9charmonicxe2x80x9d waveforms by employing a Fourier analysis of the composite waveform.
FIG. 2B is a graph similar to the graph of FIG. 2A, and illustrates a first (1st), a second (2nd) and a third (3rd) harmonic of the composite waveform 202 of FIG. 2A. The first harmonic waveform comprises a single sine wave (between 0 and 360 degrees), the second harmonic waveform comprises two sine waves (between 0 and 360 degrees), the third harmonic waveform comprises three sine waves (between 0 and 360 degrees) and, generally, the xe2x80x9cNthxe2x80x9d harmonicxe2x80x9d comprises N sine waves between 0 and 360 degrees. Together, these constituent harmonic waves, weighted by their respective amplitudes, substantially constitute the original composite measured waveform when added together.
Returning to FIG. 2A, a low amplitude on the composite waveform 202 represents a xe2x80x9csoft spotxe2x80x9d on the tire. Two such soft spots 210 and 212 are identified on the waveform 202. Similarly, a high amplitude on the composite waveform 202 represents a xe2x80x9chard spotxe2x80x9d on the tire. One such hard spot 214 is identified on the waveform 202. A peak-to-peak magnitude between the soft spots and the hard spot(s) is indicative of a uniformity characteristic of the tire, and may be used as an input parameter for tire uniformity correction, which is discussed in greater detail hereinbelow. For example, as shown in FIG. 2A, there is approximately a 7 daN peak-to-peak variation between the soft spot 210 and the hard spot 214. Similar high and low amplitude force measurements are evident on the harmonic waves illustrated in FIG. 2B, are similarly indicative of tire uniformity characteristics, and may also be used as input parameters for tire uniformity correction.
Generally, if the uniformity characteristic of the tire has a magnitude which is less than a predetermined relatively low minimum threshold magnitude, which is deemed not to be detrimental to a vehicle ride or produce undesirable vibrations in the vehicle, the tire may be shipped to a customer. If the uniformity characteristic magnitude is greater than a predetermined relatively high maximum threshold magnitude, the tire may be scrapped. If the uniformity characteristic magnitude is between the relatively low minimum threshold magnitude and the relatively high maximum threshold magnitude, the tire may be suitable for correction.
Various analytical methods may be employed to determine whether the tire needs to be (and can be) xe2x80x9ccorrectedxe2x80x9dxe2x80x94in other words, its uniformity improvedxe2x80x94based on determinations of:
a. the peak-to-peak value of the harmonic waveform or of the composite waveform (as discussed hereinabove with respect to FIGS. 2A and 2B);
b. the first and second derivatives of radial and lateral waveforms (force variation curves), as compared with predetermined specifications (thresholds) (see, e.g., U.S. Pat. No. 5,639,962); or
c. the mean or root-mean-square of a low-band filtered variation function (see, e.g., U.S. Pat. No. 4,702,103).
Techniques for correcting tire uniformity can be grouped into two general categoriesxe2x80x94xe2x80x9cgrindingxe2x80x9d, and xe2x80x9cwithout grindingxe2x80x9d.
Grinding techniques typically involve grinding of tread rubber about the outer circumference of the tire at a selected location and up to 180 degrees about the outer circumference of the tire. Grinding of the tire can contaminate a tire plant environment, reduce the useful tread life of the tire or may render the tire visually unappealing. Examples of grinding techniques and methodologies may be found in U.S. Pat. No. 3,739,533, U.S. Pat. No. 3,848,368, U.S. Pat. No. 3,946,527, U.S. Pat. No. 4,736,546, U.S. Pat. No. 4,173,850, U.S. Pat. No. 4,536,054, U.S. Pat. No. 4,458,451, U.S. Pat. No. 4,458,451, U.S. Pat. No. 4,095,374, U.S. Pat. No. 5,022,186, U.S. Pat. No. 3,848,368, U.S. Pat. No. 3,880,556, U.S. Pat. No. 3,948,004, and WO 98/05937.
A number of techniques for correcting (e.g., improving, altering) tire uniformity without grinding are known, as follows.
U.S. Pat. No. 2,963,737 (Soderquist; 1960) discloses a machine for tire manufacture (post inflation). A method is described for preventing ply shrinkage and consequent tire distortion and cracked tread rubber in tires with nylon and synthetic plies. After vulcanizing at 315-350 degrees Fahrenheit, the tire is rimmed up at its beads (not supported by its tread to avoid distortion) and post-inflated at 50-60 psi while rotating (to avoid uneven cooling) at 10-20 rpm and being sprayed until it cools to 200 degrees Fahrenheit.
U.S. Pat. No. 3,039,839 (Waters, et al.; 1962) discloses a method of making tires, and addresses issues of tire shrinkage and distortion caused by shrinkage of nylon ply cords when removed from a mold without first being allowed to cool. As mentioned therein, when nylon cord tires are removed hot from the mold, the nylon cord in the tire plies tends to shrink and distort the tire from its molded shape. It is disclosed in this patent to narrow the bead set (bead spacing when on a tire building drum) to stretch the cords during molding. Then, upon removal of the hot tire from the mold, the tire is promptly mounted on an inflating rim, and retained inflated until it cools to below the nylon cord""s shrinkage temperature of about 200 degrees Fahrenheit. This overcomes the objectionable shrinkage of cords in the tires, and an objectionable tire growth when the tires are run in service.
U.S. Pat. No. 3,389,193 (Hughes; 1968) discloses method and apparatus for shaping a deformed tire. The tire is heated in an oven to about 135 degrees Fahrenheit, and is then passed to a xe2x80x9ctire shaping machinexe2x80x9d where the uninflated tire is supported vertically on its tread by circumferentially spaced rollers (from below). Four idler pressure rollers (from above) apply pressure in a direction to cause the tread to buckle inwardly while rotating.
U.S. Pat. No. 3,464,264 (French; 1969) discloses a pneumatic tire run-in machine for removing temporary casing distortions, including flat spots. The tire is inflated, suspended and rotated within a plurality of rollers arranged around a circle with at least one of the rollers driving the tire. The small diameter of the rollers increases tire distortion and generates a large amount of heat, without requiring an external heating apparatus.
U.S. Pat. No. 3,529,048 (Kovac, et al.; 1968) discloses a method for processing of pneumatic tires wherein a tire is conditioned after being removed from the vulcanizing mold and before cooling to ambient temperature by applying a load, such as a radial load, to the tire tread while the tire is inflated and at the same time relatively moving the load along the tire, such as by rotating the tire, to cause deflection (alternate stressing and relieving of tire cords) along successive circumferential increments, all around the circumference of the tire. The conditioning steps are begun as quickly as possible, not more than within a few minutes, after the tire is removed from the mold, and the tire is conditioned for a time period of from one to two times the duration of the vulcanizing mold cycle, and the inflation pressure of the tire during conditioning is preferably of the general order of the service pressure of the tire. The exterior load on the tire being conditioned may be a radially inwardly directed radial load applied to the outside circumference of the tire. Alternatively, the exterior load may be a lateral load against the sidewall of the tire. Alternatively, the exterior load may be an oblique load (having radial and lateral force components) against the tire tread, shoulder or sidewall. The conditioning steps help obtain a more uniform tension in the tire cords while the curing or vulcanizing process continues while the hot tire is being cooled after removal from the mold. As noted in the patent, it is believed that the tire conditioning process may have one or more of the following actions on the hot tire for improving the uniformity of the tire.
xe2x80x9cFirst, the aforementioned tire cords [cotton, rayon, nylon, polyester, or other man-made synthetic or textile cord] capable of exhibiting permanent changes in physical properties upon application of load and heat are alternatively stretched by the load and relaxed while hot to make generally uniform the stress in the fibers thereof . . . . Second, any of the separate plies or belt of the tire cords in the tire may move relative either to the other plies or belt or to the surrounding rubber to make uniform the stresses therebetween. Third, different portions of any kind of tire cord in any belt or ply may move relative to each other or to portions of surrounding rubber to make generally uniform the stresses in the cord in the tire even though the cord does not permanently change its physical characteristics.xe2x80x9d (column 2, line 72 through column 3, line 18)
U.S. Pat. No. 3,632,701 (Devitt, et al.; 1972) discloses conditioning of tires to improve uniformity. Excessive radial force variations in a tire can be reduced by heating all or part of a tire while supported vertically and positioned so that the area of maximum force is located in the top quadrant of the tire. A suitable source such as a pot heater, rubber kiln or infrared heat may be used for heating. An elevated temperature (e.g., 150-280 degrees Fahrenheit) is maintained for a period of time (e.g., 60 minutes) while the tire is inflated to a pressure of 0-50 psi. The technique is applicable to nearly all types of tires including radial, belted bias, and bias tires containing rayon, nylon or polyester cords.
U.S. Pat. No. 3,635,610 (Hall, et al.; 1972) discloses a tire conditioning apparatus for removing flat spots and other surface irregularities from tires preliminary to recapping or truing them. Stress-producing conditions, including varying rates of cure applied after initial curing in the mold, the weight of a vehicle at rest, and the weight of tires pressing against other tires in a stack of tires, may cause flat spots and surface irregularities in the tires. An uninflated tire is rotated, heated, and pressed by a pressure roll assembly which has for its function flexing the tire and kneading it to work out the flat spots and surface irregularities in the tire.
U.S. Pat. No. 3,725,163 (Hofelt, Jr.; 1973) discloses a method of improving performance characteristics of pneumatic tires. Radial and lateral force variations are reduced by applying a small amount of material to portions of the tread area. This patent describes an exemplary apparatus for measuring these force variations and is exemplary of a number of patents involving the addition of material to a tire to improve a uniformity characteristic thereof.
U.S. Pat. No. 3,838,142 (Hochstein; 1974) discloses a procedure for correcting radial force variation in pneumatic tires using ionizing radiation of high energy electrons. A load drum is forced at normal operating load against the tread surface of an inflated rotating tire, and a force transducer measures the magnitude of force against the drum. The radiation source irradiates sections of the tread body and/or sidewalls which exert low force to increase their ply modulus of elasticity in those sections. The irradiation is done concurrently with the measuring.
U.S. Pat. No. 3,865,527 (McGhee, et al.; 1975) discloses tire conditioning and truing apparatus which xe2x80x9cconditionsxe2x80x9d a tire to remove flat spots by heating its sidewalls while it is uninflated and rotating. See also related U.S. Pat. No. 3,945,277 (McGhee, et al.; 1976).
U.S. Pat. No. 3,872,208 (Brown, et al.; 1975) discloses corrective heating of pneumatic tires. Radial force variation of a cured tire are reduced by selectively heating the innerliner (from inside the tire) in an area adjacent to excessive radial force variation for a predetermined time or to reach a predetermined temperature (typically 225-240 degrees Fahrenheit). The tire mounted on a support flange (not a rim) by its bead, is uninflated, and is positioned vertically with the heated portion positioned upward. See also related U.S. Pat. No. 3,880,556 (Brown, et al.; 1975).
U.S. Pat. No. 4,420,453 (Doi, et. al.; 1984) discloses apparatus for measuring tire uniformity. A tire is removed from the mold, held uninflated until it cools to 149 degrees Celsius, and then post inflated until cooled to below 90 degrees Celsius, while being supported solely by its bead edges. This allows the cord modulus to increase dramatically before inflating, and reduces the tendency for sidewall waviness as compared with a tire which is post-inflated immediately after molding.
U.S. Pat. No. 5,060,510 (Rosseau; 1991) discloses a method of correcting variations in radial force between a tire and the ground. The correction is effected by means of wedges in the form of circular rings placed between the mounting rim and the beads of the tire. The thickness of the wedge, at various positions around the tire, is related to the measure of force variation.
U.S. Pat. No. 5,365,781 (Rhyne; 1994; ""781 Patent) discloses tire uniformity correction without grinding. A tire is tested for uniformity and an electrical signal is generated, as described hereinabove. Then, tire uniformity is corrected by stretching at least a portion of at least one carcass reinforcing member beyond its elastic limit for a predetermined time, thereby permanently deforming the at least one, and preferably many, carcass reinforcing members, either by inflating the tire to a significantly raised pressure or by mechanical means. The stretching results in a permanent lengthening (elongation) of the carcass reinforcing member by a predetermined amount in the range of 0.1 to 2 or 3 percent and at a location which are a function of the measured uniformity characteristic. The techniques are generally applicable to correcting a uniformity characteristic in a cured tire. As noted in the ""781 Patent, materials of the carcass reinforcing member(s) such as nylon and polyester are readily adaptable to correction by the present invention. Materials such as polyester, steel, Kevlar (tm) and rayon are not as easily permanently elongated and may require higher pressure or longer hold time. Selected ones of the techniques for uniformity correction set forth in the ""781 Patent are discussed hereinbelow with respect to FIGS. 3, 3A, 4, 5 and 6.
FIGS. 3A and 3B (comparable to FIG. 8 and FIG. 9, respectively, of the ""781 patent) illustrate a tire being corrected for uniformity, according to a technique such as is described in the ""781 Patent.
The tire 300 (compare 100) includes a pair of annular, inextensible beads 302 and 304 (compare 102 and 104), each of which is disposed within a respective bead portion 306 and 308 (compare 106 and 108) of the tire 300, and includes a generally cylindrical tread portion 310 (compare 110), (optionally) a belt structure (xe2x80x9cbeltsxe2x80x9d) 312 (compare 112) disposed within the tread portion 310, and sidewall portions 314 and 316 (compare 114 and 116) extending between opposite sides 310a and 310b (compare 110a and 110b) of the tread portion 310 and respective ones of the beads 302 and 304. The tire 300 has a section height SH, an equatorial plane EP and an axis of rotation A. An inner liner (not shown) is disposed on the inner surface 318 of the tire 300. The tire has an outer surface 319.
At least one carcass reinforcing member 320 (or xe2x80x9cplyxe2x80x9d, compare 120) extends between the two beads 302 and 304, through the carcass of the tire. The carcass reinforcing member 320 has a central portion 320a (compare 120a) which is disposed between the two beads 302 and 304, and has two opposite end portions (xe2x80x9cturn-upxe2x80x9d ends) 320b and 320c (compare 120b and 120c), which wrap around a respective one of the beads 302 and 304 and extend radially back toward the tread portion 310 of the tire 300. The tire 300 may further include bead filler apexes (not shown, compare 122 and 124) disposed atop respective ones of the beads 302 and 304 and extending radially outwardly therefrom.
In a tire which has cooled down after being molded, the turn-up ends 320b and 320c are, for purposes of this discussion of a tire uniformity correction technique, essentially xe2x80x9cattachedxe2x80x9d to a respective one of the beads 302 and 304 and, as will be described in greater detail hereinbelow, the central portion 320a of the carcass reinforcing member 320 is essentially xe2x80x9cattachedxe2x80x9d to the belt structure 312.
Relevant portions of a tire uniformity correction machine (apparatus) are shown and described, as follows, as well as a technique for performing uniformity correction.
The tire 300 is mounted to a rim-like structure comprising two rim halves 322 and 324. The bead portions 306 and 308 engage the rim halves 322 and 324 in an airtight manner so that the tire 300 can be inflated.
Restraint rings 332 and 334 engage sidewalls 314 and 316, respectively, of a tire 300 with different axial displacements D1 and D2, respectively, to impart a different radius of curvature R1 and R2, respectively, to portions of the carcass reinforcing member 320 (best viewed in FIG. 3A) in each of the sidewalls, approximately halfway between a respective bead and the belt structure 312. As best viewed in FIG. 3B, the restraint ring 332 deflects the sidewall 314 of the tire 300 from an undeflected configuration (shown in dashed lines) axially inwardly (toward the opposite sidewall of the tire). The sidewall-contacting surfaces of the restraint rings 332 and 334 may be rounded to avoid sharp edges being in contact with the sidewalls 314 and 316, respectively, of the tire 300. Each restraint ring 332 and 334 has a radial length of engagement LE1 (best viewed in FIG. 3B) with the sidewall 314 of the tire 300 which is a relatively small percentage (i.e. less than 25%) of the section height SH of the tire 300. The restraint rings 332 and 334 may each preferably have a flat or planar surface 332a and 334a, respectively, urging against a respective sidewall 314 and 316 of the tire 300, for use in correction of a first harmonic or composite of radial force variation or in correction of conicity.
With the restraint rings 332 and 334 fixed in place and with the sidewalls 314 and 316 deflected, as shown, the tire 300 is inflated with a relatively high inflation pressure (INFLATION PRESSURE), such as 100 pounds per square inch (psi) or 7 bars. This will create a load in the carcass reinforcing member 320 thereby stretching beyond its elastic limit and permanently deforming the carcass reinforcing member 320 by an amount and at a location which are functions of the measured uniformity characteristic, resulting in a permanent lengthening (elongation) of the carcass reinforcing member to thereby correct (improve) the uniformity characteristic of the tire 300. A belt restraint ring 336 (omitted from the view of FIG. 3B) may be optionally provided in contact with the tread portion 310 to counteract the relatively high inflation pressures so that the belt structure 312 is not excessively expanded in the circumferential direction.
As best viewed in FIG. 3B, the carcass reinforcing member 320 has an upper end point 320d at which load in the carcass reinforcing member is transmitted to the belt structure 312 of the tire 300, and has a lower end point 320e in the area of the bead 302, at which load in the carcass reinforcing member 320 is transmitted to the bead 302 of the tire 300. The radius of curvature R2 in a maximally restrained portion of the tire 300 corresponding to displacement D2 is significantly less than radius of curvature R1 in the minimally restrained portion of the tire corresponding to displacement D1. Different radii of curvature provide different tension values in respective carcass reinforcing members (320).
As best viewed in FIG. 3A, with the restraint rings 332 and 334 in place and with the relatively high inflation pressure acting upon the sidewalls 314 and 316 of the tire 300, it is apparent that the original or unrestrained radius of curvature R1 of the carcass reinforcing member 320 has changed and becomes a relatively smaller radius of curvature R2. (The larger radius of curvature R1 occurs at locations of minimum restraint around the tire 300 with a planar surface restraint ring.) Physically, the smaller radius R2 of portion of the carcass reinforcing member, when the interior of the tire 300 is subjected to the relatively high inflation pressure, will not be permanently elongated the same amount as the unrestrained portion of the carcass reinforcing member 320 having the relatively larger radius of curvature R1. Generally, for a given inflation pressure, a larger radius of curvature of a portion of the carcass reinforcing member results in a relatively higher tension acting on that portion of the carcass reinforcing member. The higher tension in portions of the carcass reinforcing member 320 generally results in a relatively greater elongation above the elastic limit of the carcass reinforcing member 320 which results in its permanent elongation.
The ""781 Patent discloses a number of variations on and applications for the technique and apparatus described hereinabove, some of which are described hereinbelow with respect to FIGS. 4, 5 and 6. For example, when the first harmonic radial force variation is caused by tire attributes other than radial runout, it may be necessary to introduce a radial runout to reduce the magnitude of the first harmonic radial force variation. For example, rather than having a flat planar surface 332a on the restraint ring (e.g., 332), the restraint ring may have a cupped segment extending, for example, over a 90 degree arc length of the restraint ring so as to provide nonlinear restraint to the sidewall of the tire.
FIG. 4 (comparable to FIG. 15 of the ""781 Patent) illustrates a tire being corrected for uniformity, according to a technique such as is described in the ""781 Patent. This technique is generally similar to the technique described with respect to FIGS. 3A and 3B. A tire 400 is essentially identical to the tire 300 in that it has a tread portion 410 (compare 310), a bead 402 (compare 302) in a bead portion 406 (compare 306), (optionally) a belt structure 412 (compare 312) in the tread portion 410, a sidewall 414 (compare 314), an inner surface 418, and an outer surface 419.
At least one carcass reinforcing member 420 (compare 320) extends between the two beads of the tire 400, only one 402 of which is visible in FIG. 4, through the carcass of the tire, and has a central portion 420a (compare 320a) and two opposite end portions (xe2x80x9cturn-upxe2x80x9d ends), one 420b of which is visible in FIG. 4, which wrap around a respective one of the beads 402 and extend radially back toward the tread portion 410 of the tire 400. For purposes of this discussion, the tire 400 is assumed to already have cooled down after being molded, in which case the carcass reinforcing member 420 has an upper end point 420d (compare 320d) at which load in the carcass reinforcing member is transmitted to the belt structure 412 of the tire 400, and has a lower end point 420e (compare 320e) in the area of the bead 402, at which load in the carcass reinforcing member 420 is transmitted to the bead 302 of the tire 400.
The tire 400 is mounted to a rim-like structure comprising two rim halves, a one 422 (compare 322) of which is visible in FIG. 4. A restraining ring 432 (compare 332) having a flat surface 432a (compare 332b) is urged against the sidewall 414 of the tire 400, and has a radial length of engagement LE2 (compare LE1) which is a relatively large (e.g., greater than 25%) percentage of the section height (SH) of the tire 400, resulting in a radius of curvature R3 which is less than the initial (unrestrained) radius of curvature R1. In a manner similar to the technique described hereinabove with respect to FIGS. 3A and 3B, an elevated air pressure (AIR PRESSURE) within the tire 400 provides the motive force for stretching the carcass reinforcing member 420 beyond its elastic limit, resulting in its permanent elongation.
FIG. 5 (comparable to FIG. 11 of the ""781 Patent) illustrates a portion of a carcass reinforcing member 520 (compare 420) of a tire (not shown, compare 400) being corrected for uniformity. As in the previous examples, the carcass reinforcing member 520 (compare 420) has an upper end point 520d (compare 420d) which is essentially xe2x80x9cattachedxe2x80x9d to the belt structure (not shown), and a lower end point 520e (compare 420e) which is essentially xe2x80x9cattachedxe2x80x9d to one of the beads (not shown) of the tire.
In this example, a sidewall of the tire, hence the carcass reinforcing member 520, is restrained at two radially-separated locations, one location 542 being near the tire""s belt (and adjacent the point 520d) the other location 544 being near the tire""s bead (and adjacent the point 520e). This dual-location restraint is effectuated by a restraint device 530 comprising two portions 532 and 534 that contact the sidewall of the tire at the two radially separated locations 542 and 544, respectively.
The two portions 532 and 534 of the restraint device 530 are spaced apart from one another. Therefore, the sidewall of the tire has an unrestrained length xe2x80x9cULxe2x80x9d which will be deflected by the inflation pressure (INFLATION PRESSURE) during correcting. The restraint device 530 allows the carcass reinforcing member 520 to have a deflection and a radius of curvature R4 which is smaller than the initial unrestrained radius of curvature R1 under the influence of the inflation pressure. The carcass reinforcing member 520 is shown as a dashed line 520xe2x80x2 prior to inflation, and as a solid line after inflation.
The restraint device 530 may be sized so that the unrestrained length UL varies circumferentially around the tire. In this manner, the carcass reinforcing member(s) 520 may be permanently elongated during inflation a greater amount where the unrestrained length UL has a larger dimension.
FIG. 6 (comparable to FIG. 17 of the ""781 Patent) illustrates a tire being corrected for uniformity, according to a technique such as is described in the ""781 Patent. This technique differs from the techniques described hereinabove with respect to FIGS. 3, 3A, 4 and 5 in that the carcass reinforcing member 620 (compare 520) is stretched by mechanical means rather than by restraining the sidewall(s) of the tire and inflating the tire to a significantly raised pressure. Nevertheless, the stretching results in a comparable permanent lengthening (elongation) of the carcass reinforcing member 620.
The tire 600 is essentially identical to the tire 400 in that it has a tread portion 610 (compare 410), a bead 602 (compare 402) in a bead portion 606 (compare 406), (optionally) a belt structure 612 (compare 412) in the tread portion 610, a sidewall 614 (compare 414), an inner surface 618, and an outer surface 619.
At least one reinforcing (or xe2x80x9ccarcassxe2x80x9d) ply 620 (compare 420) extends between the two beads of the tire 600, only one 602 of which is visible in FIG. 6. For purposes of this discussion, the tire 600 is assumed to already have cooled down after being molded and, as in the previous examples, the carcass reinforcing member 620 has an upper end point 620d (compare 420d) which is essentially xe2x80x9cattachedxe2x80x9d to the belt structure 612, and a lower end point 620e (compare 420e) which is essentially xe2x80x9cattachedxe2x80x9d to one 602 of the beads of the tire 600.
A mechanical means 630 for stretching and permanently elongating the carcass reinforcing member 620 comprises the following elements:
a. elements 632 and 634 (compare 422) which hold the bead portion 606 of the tire 600;
b. an element 636 which holds the tread portion 610 of the tire 600; and
c. an element 638 which pushes axially outwardly on the sidewall 614 of the tire 600.
The tire 600 is shown with the element 638 stretching the sidewall 614 of the tire 600 axially outwardly to elongate and permanently deform the carcass reinforcing member, as discussed hereinabove. The pre-stretched carcass reinforcing member 620 is illustrated by the dashed line 620xe2x80x2. The force applied by the element 638 to the sidewall 614 of the tire 600, to deflect the sidewall 614 and stretch the carcass reinforcing member 620, is directed parallel to the axis of rotation of the tire at a position on the inside surface of the sidewall 614 which is approximately halfway between the bead 602 and the belt structure 612. Therefore, the force is substantially xe2x80x9cnormalxe2x80x9d (e.g., at 90 degrees) to the surface of the sidewall (or radial with respect to the curvature of the sidewall, as distinguished from radial with respect to the tire""s axis of rotation). It is disclosed in the ""781 Patent (see, e.g. FIG. 19 and related discussion therein) that, in an alternate embodiment of stretching the carcass reinforcing member by a mechanism, mechanical stretching of the carcass reinforcing member beyond its elastic limit can be accomplished by radially (with respect to the tire""s axis of rotation) stretching the carcass reinforcing member between its upper 620d and lower 620e attachment points, such as by moving the lower attachment point 620e radially inward and the attachment point 620d radially outward. It is also disclosed in the ""781 Patent that stretching the carcass reinforcing members could be accomplished by a combination of mechanical stretching and by inflation pressure stretching.
There have thus been described a number of techniques for correcting tire uniformity. Generally, in all of the techniques describe hereinabove with respect to FIGS. 3A, 3B, 4, 5 and 6, tire uniformity correction may be achieved only by stretching a carcass reinforcing member (e.g., the cords of the ply) beyond its elastic limit, thereby permanently deforming and elongating the carcass reinforcing member. This may reduce the ply""s strength, fatigue resistance, and adhesion to the rubber. Also, the forces required to permanently deform the carcass reinforcing members, whether applied by pressure or by mechanical devices, will exert tremendous stress on the beads. More generally, it should be appreciated that it is generally undesirable to stretch an elastic member to the point where it permanently deforms, since this may adversely affect the elastic member""s subsequent ability to exert and/or react forcesxe2x80x94in other words, to act in an elastic mode in a predicable manner. (Consider, for example, the case of a stretched out elastic waistband on a garment.) In a worst case, the elastic member may be stretched to the point that it breaks, rendering it essentially useless.
Another nuance of the stretching/deforming techniques described hereinabove with respect to FIGS. 3A, 3B, 4, 5 and 6 is that the tire (e.g., 300) must first be cooled down from the molding process sufficiently that the carcass reinforcing member (e.g., 320) is essentially attached at its ends (e.g., 320d and 320e) between the belt (e.g., 312) and the bead (e.g., 302) and can be stretched and deformed between those two ends.
Another nuance of the stretching/deforming techniques described hereinabove with respect to FIGS. 3A, 3B, 4, 5 and 6 is that a tire which has been corrected in such a manner may be required to sit for a period of time (xe2x80x9csit periodxe2x80x9d), for example twenty four hours, sufficient to take into consideration any viscoelastic relaxation that occurred in the tire after correction, after which time period it may be necessary to re-test the tire for uniformity.
As mentioned above, cords of a carcass reinforcing member (ply) may be made of a variety of materials, including nylon, polyester, steel, Kevlar (tm) and rayon. According to the ""781 Patent, the stretching/deforming techniques disclosed therein are not as readily adaptable to correcting tires with steel (metal), Kevlar (tm) and rayon cords.
What is therefore needed is a technique for tire uniformity correction, without grinding, which does not permanently deform the cords of a carcass reinforcing member beyond their elastic limit, which can be utilized on tires having any of a variety of cord materials, which can possibly be performed on a xe2x80x9chotxe2x80x9d tire (one which has not completely cooled down from the molding process) and which does not require a xe2x80x9csit periodxe2x80x9d.
It is an object of the present invention to provide methods and apparatuses for correcting one or more uniformity characteristics of a pneumatic tire by changing the tension characteristics of the tire under normal inflation.
The present invention relates to a tire construction and method of correcting one or more tire uniformity characteristics. The tire has two beads and a carcass reinforcement ply having reinforcement cords. The method is characterized by the steps of A) forming a portion of the tire with a material that can be rendered plastic and rendered non-plastic, which, in turn, respectively permits and restricts reorientation of the reinforcement cords; B) rendering the material plastic, after the tire has been vulcanized, to permit one or more of the reinforcement cords to be reoriented; C) reorienting one or more reinforcement cords with respect to other reinforcement cords or components; and D) rendering the material nonplastic, to restrict further reorientation of adjacent reinforcement cords. Reorientation of the cords can be achieved without stretching them beyond their elastic limit.
The material can be a thermoplastic, in which case, it is rendered plastic by being heated above its deflection temperature, and rendered nonplastic by cooling below its deflection temperature. It is possible to heat selected portions of the tire to permit reorientation of reinforcement cords, for example in response to measured tire uniformity characteristics. Reorientation of cords can include the cords slipping with respect to the bead. Reorientation of cords can be achieved through applying a force to the tire""s sidewall, such as through inflating the tire above its recommended operating pressure and restraining the force at different locations as a function of measured uniformity data. The material""s deflection temperature is preferably less than 190 degrees C. and preferably over 121 degrees C. The thermoplastic material can be disposed between the bead and an adjacent portion of the carcass reinforcement ply, such as in the form of a layer extending around the bead. Alternatively, the thermoplastic material can comprise a portion of the tire""s apex or a portion of the bead""s matrix that encases bead""s steel filaments.
Other objects, advantages and features of the invention will become apparent in light of the following descriptions thereof.